Degeneracy and strong fluctuation-induced first-order phase transition in the dipolar pyrochlore antiferromagnet

Abstract

We show that a continuous set of degenerate critical soft modes strongly enhances the first-order character of a fluctuation-induced first-order transition in the pyrochlore dipolar Heisenberg antiferromagnet. Such a degeneracy seems essential to explain the strong first-order transition recently observed in Gd₂Sn₂O₇. We present some evidence from Monte Carlo simulations and a perturbative renormalization group expansion.